Multi-path layer configured for detection and mitigation of slow drain issues in a storage area network

ABSTRACT

A processing device is configured to control delivery of input-output (IO) operations from a host device to a storage system over selected ones of a plurality of paths through a network, and to monitor response times for particular ones of the IO operations sent from the host device to the storage system. The processing device is further configured, responsive to at least a subset of the monitored response times being above a threshold over a time period, to generate an alert, to send the alert to an intermediary device coupled to the host device and the storage system, to receive from the intermediary device a throttling command generated in the intermediary device based at least in part on the alert, and responsive to receipt of the throttling command, to at least temporarily reduce a rate at which additional ones of the IO operations are sent from the host device to the storage system.

FIELD

The field relates generally to information processing systems, and more particularly to storage in information processing systems.

BACKGROUND

Storage arrays and other types of storage systems are often shared by multiple host devices over a network. Applications running on the host devices each include one or more processes that perform the application functionality. The processes issue input-output (IO) operations directed to particular logical storage volumes or other logical storage devices, for delivery by the host devices over selected paths to storage ports of the storage system. Different ones of the host devices can run different applications with varying workloads and associated IO patterns. Such host devices also generate additional IO operations in performing various data services such as migration and replication. Various types of storage access protocols can be used by host devices to access the logical storage volumes or other logical storage devices of the storage system, including by way of example Small Computer System Interface (SCSI) access protocols and Non-Volatile Memory Express (NVMe) access protocols. In these and other storage systems, problems can arise when paths from one or more of the host devices to the storage system experience performance degradations. For example, such performance degradations can include “slow drain” issues potentially arising from imbalances in supported data rates between host devices, network switches and storage arrays.

SUMMARY

Illustrative embodiments disclosed herein provide techniques for detection and mitigation of slow drain issues. In some embodiments, the techniques are implemented at least in part in a multi-path layer of at least one host device configured to communicate over a network with one or more storage arrays or other types of storage systems.

The multi-path layer illustratively comprises at least one multi-path input-output (MPIO) driver configured to process IO operations of at least one host device that communicates with one or more storage arrays or other types of storage systems over designated paths through a storage area network (SAN) or other type of network.

Other types of host drivers or other host device components can be used in place of or in addition to one or more MPIO drivers in implementing functionality for detection and mitigation of slow drain issues as disclosed herein.

In one embodiment, an apparatus comprises at least one processing device that includes a processor and a memory, with the processor being coupled to the memory. The at least one processing device is configured to control delivery of IO operations from a host device to a storage system over selected ones of a plurality of paths through a network, and to monitor response times for particular ones of the IO operations sent from the host device to the storage system. The processing device is further configured, responsive to at least a subset of the monitored response times being above a threshold over a time period, to generate an alert, to send the alert to an intermediary device coupled to the host device and the storage system, to receive from the intermediary device a throttling command generated in the intermediary device based at least in part on the alert, and responsive to receipt of the throttling command, to at least temporarily reduce a rate at which additional ones of the IO operations are sent from the host device to the storage system.

The at least one processing device illustratively comprises at least a portion of the host device. Other embodiments can include multiple host devices, with each such host device implementing similar functionality.

In some embodiments, the paths are associated with respective initiator-target pairs, with the initiators of the initiator-target pairs illustratively comprising respective host bus adaptors (HBAs) of the host device and the targets of the initiator-target pairs illustratively comprising respective storage array ports of the storage system. Other types of paths involving other types of initiators and targets can be used in other embodiments.

In some embodiments, the at least one processing device comprises at least one MPIO driver implemented in the host device and configured to control delivery of IO operations to storage devices of the storage system over selected ones of the plurality of paths through the network. For example, the MPIO driver is illustratively configured to perform at least a portion of the monitoring of response times, the generating of the alert, the sending of the alert, the receiving of the throttling command, and the at least temporarily reducing of the rate, as well as additional or alternative functionality.

The throttling command in some embodiments is generated in the intermediary device based at least in part on identification in the intermediary device of one or more of the plurality of paths that each exhibits at least a threshold amount of mismatch between a negotiated rate of its initiator and a negotiated rate of its target. For example, the mismatch between the negotiated rate of the initiator and the negotiated rate of the target illustratively comprises the negotiated rate of the initiator being less than the negotiated rate of the target, although other types of mismatches may additionally or alternatively exist.

The at least one processing device in some embodiments is further configured to send negotiated rate information of respective initiators of the host device to the intermediary device for utilization by the intermediary device in generating the throttling command.

In some embodiments, the intermediary device illustratively comprises an MPIO management station that is coupled to the MPIO driver of the host device and to MPIO drivers of respective ones of one or more additional host devices coupled to the storage system.

Additionally or alternatively, the intermediary device comprises at least one server configured to obtain negotiated rate information for respective initiators from the host device and one or more additional host devices coupled to the storage system, and to obtain negotiated rate information for respective targets from the storage system, for utilization by the intermediary device in generating the throttling command.

For example, the intermediary device illustratively obtains the negotiated rate information for respective initiators from the host device via an operating system (OS) native command line interface (CLI), and the intermediary device illustratively obtains the negotiated rate information for respective targets from the storage system via a representational state transfer (REST) call to the storage system.

In some embodiments, the throttling command is generated in the intermediary device responsive to a determination that the host device exhibits a greater degree of mismatch between one or more of its initiator negotiated rates and one or more corresponding target negotiated rates of the storage system than at least one other host device coupled to the storage system.

The at least one processing device in some embodiments is further configured to receive from the intermediary device an additional command generated in the intermediary device, and responsive to receipt of the additional command, to at least partially reverse the reduction in the rate at which additional ones of the IO operations are sent from the host device to the storage system.

These and other illustrative embodiments include, without limitation, apparatus, systems, methods and computer program products comprising processor-readable storage media.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an information processing system configured with functionality for detection and mitigation of slow drain issues in an illustrative embodiment.

FIG. 2 is a flow diagram of a process for detection and mitigation of slow drain issues in an illustrative embodiment.

FIG. 3 is a block diagram showing multiple layers of a layered system architecture that incorporates functionality for detection and mitigation of slow drain issues in an illustrative embodiment.

FIG. 4 shows an example data structure utilized in implementing detection and mitigation of slow drain issues in an illustrative embodiment.

FIG. 5 is a block diagram illustrating an example interconnection arrangement between a management station, multiple host devices and a storage array in an illustrative embodiment.

DETAILED DESCRIPTION

Illustrative embodiments will be described herein with reference to exemplary information processing systems and associated computers, servers, storage devices and other processing devices. It is to be appreciated, however, that embodiments of the present disclosure are not restricted to use with the particular illustrative system and device configurations shown. Accordingly, the term “information processing system” as used herein is intended to be broadly construed, so as to encompass, for example, processing systems comprising cloud computing and storage systems, as well as other types of processing systems comprising various combinations of physical and virtual processing resources. An information processing system may therefore comprise, for example, at least one data center that includes one or more clouds hosting multiple tenants that share cloud resources. Numerous other types of enterprise and cloud-based computing and storage systems are also encompassed by the term “information processing system” as that term is broadly used herein.

FIG. 1 shows an information processing system 100 configured in accordance with an illustrative embodiment. The information processing system 100 comprises a computer system 101 illustratively comprising a plurality of host devices 102-1, . . . 102-N. The host devices 102 communicate over a storage area network (SAN) 104 with at least one storage array 105. The storage array 105 comprises a plurality of storage devices 106-1, . . . 106-M each storing data utilized by one or more applications running on one or more of the host devices 102. The storage devices 106 are illustratively arranged in one or more storage pools.

The storage array 105 and its associated storage devices 106 are an example of what is more generally referred to herein as a “storage system.” This storage system in the present embodiment is shared by the host devices 102, and is therefore also referred to herein as a “shared storage system.” Other embodiments can include only a single host device, possibly configured to have exclusive use of the storage system.

The host devices 102 illustratively comprise respective computers, servers or other types of processing devices capable of communicating with the storage array 105 over the SAN 104. For example, at least a subset of the host devices 102 may be implemented as respective virtual machines of a compute services platform or other type of processing platform. The host devices 102 in such an arrangement illustratively provide compute services such as execution of one or more applications on behalf of each of one or more users associated with respective ones of the host devices 102.

The term “user” herein is intended to be broadly construed so as to encompass numerous arrangements of human, hardware, software or firmware entities, as well as combinations of such entities.

Compute and/or storage services may be provided for users under a Platform-as-a-Service (PaaS) model, an Infrastructure-as-a-Service (IaaS) model and/or a Function-as-a-Service (FaaS) model, although it is to be appreciated that numerous other cloud infrastructure arrangements could be used. Also, illustrative embodiments can be implemented outside of the cloud infrastructure context, as in the case of a stand-alone computing and storage system implemented within a given enterprise.

The storage devices 106 of the storage array 105 of SAN 104 implement logical units (LUNs) configured to store objects for users associated with the host devices 102. These objects can comprise files, blocks or other types of objects. The host devices 102 interact with the storage array 105 utilizing read and write commands as well as other types of commands that are transmitted over the SAN 104. Such commands in some embodiments more particularly comprise Small Computer System Interface (SCSI) commands of a SCSI access protocol and/or Non-Volatile Memory Express (NVMe) commands of an NVMe access protocol, although other types of commands can be used in other embodiments. A given IO operation as that term is broadly used herein illustratively comprises one or more such commands. References herein to terms such as “input-output” and “IO” should be understood to refer to input and/or output. Thus, an IO operation relates to at least one of input and output.

Also, the term “storage device” as used herein is intended to be broadly construed, so as to encompass, for example, a logical storage device such as a LUN or other logical storage volume. A logical storage device can be defined in the storage array 105 to include different portions of one or more physical storage devices. Storage devices 106 may therefore be viewed as comprising respective LUNs or other logical storage volumes.

Each of the host devices 102 illustratively has multiple paths to the storage array 105, with at least one of the storage devices 106 of the storage array 105 being visible to that host device on a given one of the paths. A given one of the storage devices 106 may be accessible to the given host device over multiple paths.

Different ones of the storage devices 106 of the storage array 105 illustratively exhibit different latencies in processing of IO operations. In some cases, the same storage device may exhibit different latencies for different ones of multiple paths over which that storage device can be accessed from a given one of the host devices 102.

The host devices 102, SAN 104 and storage array 105 in the FIG. 1 embodiment are assumed to be implemented using at least one processing platform each comprising one or more processing devices each having a processor coupled to a memory. Such processing devices can illustratively include particular arrangements of compute, storage and network resources. For example, processing devices in some embodiments are implemented at least in part utilizing virtual resources such as virtual machines (VMs) or Linux containers (LXCs), or combinations of both as in an arrangement in which Docker containers or other types of LXCs are configured to run on VMs.

The host devices 102 and the storage array 105 may be implemented on respective distinct processing platforms, although numerous other arrangements are possible. For example, in some embodiments at least portions of the host devices 102 and the storage array 105 are implemented on the same processing platform. The storage array 105 can therefore be implemented at least in part within at least one processing platform that implements at least a subset of the host devices 102.

The SAN 104 may be implemented using multiple networks of different types to interconnect storage system components. For example, the SAN 104 may comprise a portion of a global computer network such as the Internet, although other types of networks can be part of the SAN 104, including a wide area network (WAN), a local area network (LAN), a satellite network, a telephone or cable network, a cellular network, a wireless network such as a WiFi or WiMAX network, or various portions or combinations of these and other types of networks. The SAN 104 in some embodiments therefore comprises combinations of multiple different types of networks each comprising processing devices configured to communicate using Internet Protocol (IP) or other related communication protocols.

As a more particular example, some embodiments may utilize one or more high-speed local networks in which associated processing devices communicate with one another utilizing Peripheral Component Interconnect express (PCIe) cards of those devices, and networking protocols such as InfiniBand (IB), Gigabit Ethernet or Fibre Channel (FC). Numerous alternative networking arrangements are possible in a given embodiment, as will be appreciated by those skilled in the art.

The host devices 102 comprise respective sets of IO queues 110-1, . . . 110-N and respective MPIO drivers 112-1, . . . 112-N. The MPIO drivers 112 collectively comprise a multi-path layer of the host devices 102. Path selection functionality for delivery of IO operations from the host devices 102 to the storage array 105 is provided in the multi-path layer by respective instances of path selection logic 114-1, . . . 114-N implemented within the MPIO drivers 112. The multi-path layer further provides functionality for detection and mitigation of slow drain issues as disclosed herein. Such functionality is provided at least in part using respective instances of IO throttling logic 115-1, . . . 115-N implemented within the MPIO drivers 112.

The MPIO drivers 112 may comprise, for example, otherwise conventional MPIO drivers, such as PowerPath® drivers from Dell Technologies, suitably modified in the manner disclosed herein to provide functionality for detection and mitigation of slow drain issues. Other types of MPIO drivers from other driver vendors may be suitably modified to incorporate functionality for detection and mitigation of slow drain issues as disclosed herein.

The host devices 102 can include additional or alternative components. For example, in some embodiments, the host devices 102 comprise respective local caches, implemented using respective memories of those host devices. A given such local cache can be implemented using one or more cache cards, possibly implementing caching techniques such as those disclosed in U.S. Pat. Nos. 9,201,803, 9,430,368 and 9,672,160, each entitled “System and Method for Caching Data,” and incorporated by reference herein. A wide variety of different caching techniques can be used in other embodiments, as will be appreciated by those skilled in the art. Other examples of memories of the respective host devices 102 that may be utilized to provide local caches include one or more memory cards or other memory devices, such as, for example, an NVMe over PCIe cache card, a local flash drive or other type of NVM storage drive, or combinations of these and other host memory devices.

The system 100 further comprises an MPIO management station 116 that includes a processor 117 implementing interface logic 118. The interface logic 118 is utilized to communicate with the host devices 102 and the storage array 105. Such an MPIO management station 116 provides management functionality for the multi-path layer comprising the MPIO drivers 112 of the host devices 102. In some embodiments, host device management software executing on the MPIO management station 116 interacts with storage array management software executing on the storage array 105. The MPIO management station 116, or portions thereof, may be considered in some embodiments as forming part of what is referred to herein as a “multi-path layer” that includes the MPIO drivers 112 of the host devices 102. The term “multi-path layer” as used herein is intended to be broadly construed and may comprise, for example, an MPIO layer or other multi-path software layer of a software stack, or more generally multi-pathing software program code, running on one or more processing devices each comprising at least one processor and at least one memory.

The MPIO management station 116 is an example of what is more generally referred to herein as an “external server” relative to the storage array 105. Additional or alternative external servers of different types can be used in other embodiments. In some embodiments, one or more external servers, such as the MPIO management station 116, perform at least a portion of the functionality for detection and mitigation of slow drain issues as disclosed herein, illustratively in cooperation with the storage array 105 and the instances of IO throttling logic 115 of the respective MPIO drivers 112.

The MPIO driver 112-1 is configured to deliver IO operations selected from its corresponding set of IO queues 110-1 to the storage array 105 via selected ones of multiple paths over the SAN 104. The sources of the IO operations stored in the set of IO queues 110-1 illustratively include respective processes of one or more applications executing on the host device 102-1. For example, IO operations can be generated by each of multiple processes of a database application running on the host device 102-1. Such processes issue IO operations for delivery to the storage array 105 over the SAN 104. Other types of sources of IO operations may be present in a given implementation of system 100.

A given IO operation is therefore illustratively generated by a process of an application running on the host device 102-1, and is queued in a given one of the IO queues 110-1 of the host device 102-1 with other operations generated by other processes of that application, and possibly other processes of other applications.

The paths from the host device 102-1 to the storage array 105 illustratively comprise paths associated with respective initiator-target pairs, with each initiator comprising a host bus adaptor (HBA) or other initiating entity of the host device 102-1 and each target comprising a port or other targeted entity corresponding to one or more of the storage devices 106 of the storage array 105. As noted above, the storage devices 106 illustratively comprise LUNs or other types of logical storage devices.

In some embodiments, the paths are associated with respective communication links between the host device 102-1 and the storage array 105 with each such communication link having a negotiated link speed. For example, in conjunction with registration of a given HBA to a switch of the SAN 104, the HBA and the switch may negotiate a link speed. The actual link speed that can be achieved in practice in some cases is less than the negotiated link speed, which is a theoretical maximum value. A negotiated link speed is an example of what is more generally referred to herein as a “negotiated rate.”

The negotiated rates of the respective initiator and target of a particular one of the paths illustratively comprise respective negotiated data rates determined by execution of at least one link negotiation protocol for that path. The link negotiation protocol is illustratively performed separately by the initiator and the target, and involves each such component separately interacting with at least one switch of a switch fabric of the network 104 in order to determine the negotiated rate, potentially leading to substantial mismatches in initiator and target negotiated rates for the same switch, set of switches or switch fabric of the SAN 104.

The term “negotiated rate” therefore illustratively comprises a rate negotiated between an initiator or a target and a switch of a switch fabric of network 104. However, the term “negotiated rate” as used herein is intended to be broadly construed so as to also encompass, for example, arrangements that refer to negotiated speeds. Any of a wide variety of different link negotiation protocols can be used, including auto-negotiation protocols, as will be readily appreciated by those skilled in the art.

For example, some embodiments are configured to utilize link negotiation protocols that allow negotiation of data rates, such as 1G, 2G, 4G, 8G, 16G, 32G, 64G and 128G, where G denotes Gigabits per second (Gb/sec). The link bandwidth is illustratively specified in terms of Megabytes per second (MB/sec), and the actual amount of data that can be sent over the link in practice is typically somewhat lower than the negotiated data rate. Accordingly, a negotiated rate of 1G in some systems may correspond to an actual achievable data rate that is lower than 100 MB/sec, such as a rate of 85 MB/sec. Other negotiated rates referred to herein are denoted in terms of Gigabytes per second (GB/sec).

The term “negotiated rate” as used herein is therefore intended to be broadly construed, so as to encompass, for example, a theoretical negotiated rate or an actual achievable data rate that corresponds to the theoretical negotiated rate within a given system.

It is also to be appreciated that a wide variety of other types of rate negotiation may be performed in other embodiments.

As indicated previously, problems can arise when paths from one or more of the host devices 102 to the storage array 105 experience performance degradations. For example, such performance degradations can include “slow drain” issues potentially arising from imbalances in supported data rates between one or more of the host devices 102, switches of the SAN 104, and the storage array 105.

Illustrative embodiments herein detect and mitigate such slow drain issues, as will be described in more detail below.

Various scheduling algorithms, load balancing algorithms and/or other types of algorithms can be utilized by the MPIO driver 112-1 in delivering IO operations from the IO queues 110-1 to the storage array 105 over particular paths via the SAN 104. Each such IO operation is assumed to comprise one or more commands for instructing the storage array 105 to perform particular types of storage-related functions such as reading data from or writing data to particular logical volumes of the storage array 105. Such commands are assumed to have various payload sizes associated therewith, and the payload associated with a given command is referred to herein as its “command payload.”

A command directed by the host device 102-1 to the storage array 105 is considered an “outstanding” command until such time as its execution is completed in the viewpoint of the host device 102-1, at which time it is considered a “completed” command. The commands illustratively comprise respective SCSI commands, although other command formats can be used in other embodiments. A given such command is illustratively defined by a corresponding command descriptor block (CDB) or similar format construct. The given command can have multiple blocks of payload associated therewith, such as a particular number of 512-byte SCSI blocks or other types of blocks.

In illustrative embodiments to be described below, it is assumed without limitation that the initiators of a plurality of initiator-target pairs comprise respective HBAs of the host device 102-1 and that the targets of the plurality of initiator-target pairs comprise respective ports of the storage array 105. Examples of such HBAs and storage array ports are illustrated in conjunction with the embodiment of FIG. 3.

Selecting a particular one of multiple available paths for delivery of a selected one of the IO operations of the set of IO queues 110-1 is more generally referred to herein as “path selection.” Path selection as that term is broadly used herein can in some cases involve both selection of a particular IO operation and selection of one of multiple possible paths for accessing a corresponding logical device of the storage array 105. The corresponding logical device illustratively comprises a LUN or other logical storage volume to which the particular IO operation is directed.

It should be noted that paths may be added or deleted between the host devices 102 and the storage array 105 in the system 100. For example, the addition of one or more new paths from host device 102-1 to the storage array 105 or the deletion of one or more existing paths from the host device 102-1 to the storage array 105 may result from respective addition or deletion of at least a portion of the storage devices 106 of the storage array 105.

Addition or deletion of paths can also occur as a result of zoning and masking changes or other types of storage system reconfigurations performed by a storage administrator or other user. Some embodiments are configured to send a predetermined command from the host device 102-1 to the storage array 105, illustratively utilizing the MPIO driver 112-1, to determine if zoning and masking information has been changed. The predetermined command can comprise, for example, a log sense command, a mode sense command, a “vendor unique” or VU command, or combinations of multiple instances of these or other commands, in an otherwise standardized command format.

In some embodiments, paths are added or deleted in conjunction with addition of a new storage array or deletion of an existing storage array from a storage system that includes multiple storage arrays, possibly in conjunction with configuration of the storage system for at least one of a migration operation and a replication operation.

For example, a storage system may include first and second storage arrays, with data being migrated from the first storage array to the second storage array prior to removing the first storage array from the storage system.

As another example, a storage system may include a production storage array and a recovery storage array, with data being replicated from the production storage array to the recovery storage array so as to be available for data recovery in the event of a failure involving the production storage array.

In these and other situations, path discovery scans may be repeated as needed in order to discover the addition of new paths or the deletion of existing paths.

A given path discovery scan can be performed utilizing known functionality of conventional MPIO drivers, such as PowerPath® drivers.

The path discovery scan in some embodiments may be further configured to identify one or more new LUNs or other logical storage volumes associated with the one or more new paths identified in the path discovery scan. The path discovery scan may comprise, for example, one or more bus scans which are configured to discover the appearance of any new LUNs that have been added to the storage array 105 as well to discover the disappearance of any existing LUNs that have been deleted from the storage array 105.

The MPIO driver 112-1 in some embodiments comprises a user-space portion and a kernel-space portion. The kernel-space portion of the MPIO driver 112-1 may be configured to detect one or more path changes of the type mentioned above, and to instruct the user-space portion of the MPIO driver 112-1 to run a path discovery scan responsive to the detected path changes. Other divisions of functionality between the user-space portion and the kernel-space portion of the MPIO driver 112-1 are possible. The user-space portion of the MPIO driver 112-1 is illustratively associated with an Operating System (OS) kernel of the host device 102-1. Other MPIO driver arrangements are possible. For example, in some embodiments, an MPIO driver may be configured using a kernel-based implementation, and in such an arrangement may include only a kernel-space portion and no user-space portion.

For each of one or more new paths identified in the path discovery scan, the host device 102-1 may be configured to execute a host registration operation for that path. The host registration operation for a given new path illustratively provides notification to the storage array 105 that the host device 102-1 has discovered the new path.

The MPIO management station 116 is arranged as an intermediary device relative to the host devices 102 and the storage array 105. Some communications between the host devices 102 and the storage array 105 can occur via such an intermediary device, which as indicated elsewhere herein can alternatively comprise one or more external servers. Such communications illustratively involve utilization of an out-of-band communication mechanism, such as one or more IP connections between the host devices 102 and the MPIO management station 116.

As indicated previously, the host devices 102 communicate directly with the storage array 105 using one or more storage access protocols such as SCSI, Internet SCSI (iSCSI), SCSI over FC (SCSI-FC), NVMe over FC (NVMe/FC), NVMe over Fabrics (NVMeF), NVMe over TCP (NVMe/TCP), and/or others. The MPIO management station 116 in some embodiments is similarly configured to communicate directly with the storage array 105 using one or more such storage access protocols.

The MPIO driver 112-1 on the host device 102-1 illustratively has connectivity to the MPIO management station 116. The MPIO management station 116 in some embodiments implements PowerPath® Management Appliance (PPMA) functionality to obtain access to the host devices 102 and the storage array 105. The MPIO driver 112-1 can obtain from the MPIO management station 116 certain types of storage array related information for use in various operations performed at least in part by the MPIO driver 112-1, in addition to or in place of obtaining such information directly from the storage array 105. Host multi-pathing software can be used to implement a multi-path layer comprising MPIO drivers 112 of respective host devices 102 as well as related management appliance software such as the above-noted PPMA of MPIO management station 116. Such host multi-pathing software can be configured to facilitate detection and mitigation of slow drain issues as disclosed herein. For example, multi-pathing software residing on one or more of the host devices 102 (e.g., a server such as an ESXi server or an AIX server) is utilized in illustrative embodiments to support detection and mitigation of slow drain issues.

In the FIG. 1 embodiment, the storage array 105 comprises a plurality of storage controllers 120, MPIO management station interface logic 121, and one or more target port data structures 122 for storing negotiated rate information for different target ports of the storage array 105. In other embodiments, at least portions of one or more of the MPIO management station interface logic 121 and the corresponding data structures 122 can be implemented at least in part external to the storage array 105 rather than internal to the storage array 105. For example, in some embodiments at least portions of the MPIO management station interface logic 121 and corresponding data structures 122 are implemented on one or more servers that are external to the storage array 105.

Accordingly, such logic components and related stored information may be located internal to the storage array 105, external to the storage array 105, or implemented in part internally and in part externally to the storage array 105, and can include various combinations of hardware, firmware and software. The term “logic” as used herein is therefore intended to be broadly construed.

As indicated above, at least portions of the communications between the host devices 102 and the storage array 105 can utilize an in-band communication mechanism in which one or more predetermined commands in a designated storage access protocol are sent from the host device 102-1 to the storage array 105. Such predetermined commands can comprise, for example, read and/or write commands, sense commands (e.g., log sense and/or mode sense commands), “vendor unique” or VU commands, or combinations of multiple instances of these or other commands, in an otherwise standardized command format, such as a SCSI format, an NVMe format, or other type of format. A “command” as the term is broadly used herein can comprise a combination of multiple distinct commands.

It is also possible for the host devices 102 and the storage array 105 to communicate via one or more out-of-band communication mechanisms. For example, an out-of-band communication mechanism of this type can involve host management software of the host device 102-1 communicating with storage array management software of the storage array 105 over an IP network connection or other type of network connection. Such host management software can include software running on the MPIO management station 116, in addition to or in place of software running on the individual host devices 102.

Additional components not explicitly shown in the figure, such as one or more storage caches, may also be provided in the storage array 105 for use in processing IO operations. For example, in some embodiments, each of the storage controllers 120 has a different local cache or a different allocated portion of a global cache associated therewith, although numerous alternative arrangements are possible. The storage controllers 120 can be implemented as respective storage processors, directors or other storage system components configured to control storage system operations relating to processing of IO operations.

As indicated above, illustrative embodiments overcome various drawbacks of conventional practice by configuring the system 100 to include functionality for detection and mitigation of slow drain issues, as will now be described in more detail.

In operation, the MPIO driver 112-1 is configured to control delivery of IO operations from its corresponding host device 102-1 to storage array 105 over selected ones of a plurality of paths through SAN 104, using its path selection logic 114-1, where the paths are associated with respective initiator-target pairs, the initiators being implemented on the host device 102-1 and the targets being implemented on the storage array 105. The MPIO driver 112-1 in the present embodiment also monitors response times for particular ones of the IO operations sent from the host device 102-1 to the storage array 105. Responsive to at least a subset of the monitored response times being above a designated threshold over a particular time period, illustratively a specified monitoring time period, the MPIO driver 112-1 is further configured to generate an alert, to send the alert to the MPIO management station 116 coupled to the host device 102-1 and the storage array 105, to receive from the intermediary device a throttling command generated in the MPIO management station 116 based at least in part on the alert, and responsive to receipt of the throttling command, to at least temporarily reduce a rate at which additional ones of the IO operations are sent from the host device 102-1 to the storage array 105.

At least a portion of such functionality is carried out by the IO throttling logic 115-1 of the MPIO driver 112-1, possibly in cooperation with the path selection logic 114-1. For example, the path selection logic 114-1 may be configured to monitor response times and to generate and send the above-noted alert, while the IO throttling logic 115-1 is illustratively configured to receive the throttling command from the MPIO management station 116, and to reduce the rate at which IO operations are sent from the host device 102-1 over one or more of the paths in accordance with the throttling command.

The term “alert” as used herein is intended to be broadly construed, so as to encompass, for example, a wide variety of different types of commands, notifications, messages or other information that may be conveyed by a host device to an intermediary device.

Terms such as “monitoring time period” or more generally “time period” as used herein are also intended to be broadly construed, and should not be viewed as being limited to particular types of time periods having particular durations.

The MPIO management station 116 is an example of what is more generally referred to herein as an “intermediary device” coupled to the host device 102-1 and the storage array 105, and is illustratively implemented as one or more servers. Other types of servers, computers, management appliances or other intermediary devices can be used in other embodiments in addition to or in place of the MPIO management station 116. For example, as indicated previously, the MPIO management station 116 may be implemented as a PPMA configured to implement intermediary device functionality of the type disclosed herein.

The host device 102-1 is an example of what is more generally referred to herein as “at least one processing device” comprising a processor and a memory, with the processor being coupled to the memory. References herein to “at least one processing device” may instead comprise a portion of the host device 102-1, or at least a portion of multiple host devices 102, with each such host device implementing similar functionality. Other types of arrangements of one or more processing devices can be used to implement functionality for detection and mitigation of slow drain issues as disclosed herein.

The paths over which IO operations are delivered from the host device 102-1 to the storage array 105 under the control of the MPIO driver 112-1 are assumed to be associated with respective initiator-target pairs, with the initiators of the initiator-target pairs illustratively comprising respective HBAs of the host device 102-1 and the targets of the initiator-target pairs illustratively comprising respective storage array ports of the storage array 105. Other types of paths involving other types of initiators and targets can be used in other embodiments.

The throttling command in some embodiments is generated in the MPIO management station 116 based at least in part on identification in the MPIO management station 116 of one or more of the plurality of paths that each exhibits at least a threshold amount of mismatch between a negotiated rate of its initiator and a negotiated rate of its target. For example, the mismatch between the negotiated rate of the initiator and the negotiated rate of the target illustratively comprises the negotiated rate of the initiator being less than the negotiated rate of the target, although other types of mismatches may also exist.

The host device 102-1 in some embodiments is further configured to send negotiated rate information of respective HBAs or other initiators of the host device 102-1 to the MPIO management station 116 for utilization by the MPIO management station 116 in generating the throttling command. In generating such a throttling command for one of the host devices 102, such as the host device 102-1, the MPIO management station 116 takes into account mismatches between initiator and target negotiated rates on one or more other ones of the host devices 102. Accordingly, the MPIO management station 116 may generate throttling commands for multiple ones of the host devices 102, in order to mitigate slow drain issues attributable to detected mismatches involving those host devices 102.

The MPIO management station 116 is illustratively configured to obtain negotiated rate information for respective initiators from the host devices 102, and to obtain negotiated rate information for respective targets from the storage array 105, for utilization by the MPIO management station 116 in generating the throttling command.

For example, the MPIO management station 116 illustratively obtains the negotiated rate information for respective initiators from the host device 102-1 via an operating system (OS) native command line interface (CLI), and the MPIO management station 116 illustratively obtains the negotiated rate information for respective targets from the storage array 105 via a representational state transfer (REST) call to the storage array. Other techniques can be used to allow the MPIO management station 116 to obtain such negotiated rate information in other embodiments.

In some embodiments, the throttling command is generated in the MPIO management station 116 responsive to a determination that the host device 102-1 exhibits a greater degree of mismatch between one or more of its initiator negotiated rates and one or more corresponding target negotiated rates of the storage array 105 than at least one other host device coupled to the storage array 105.

The throttling command can be generated using one or more commands in a format of a designated storage access protocol, such as a SCSI access protocol or an NVMe access protocol, possibly using one or more vendor unique commands of such protocols. A wide variety of other command formats can be used, including commands sent over IP connections or other types of network connections.

The term “throttling command” as used herein is therefore intended to be broadly construed, so as to encompass, for example, information that directs at least one of the host devices 102 to “throttle” or reduce a rate at which it sends IO operations over one or more paths between the host device and the storage array 105. The throttling command may specify a particular rate reduction to be made, or may instead indicate that a rate reduction of an amount to be determined by the MPIO driver 112-1 should be made.

The MPIO driver 112-1 is further configured to receive from the MPIO management station 116 an additional command generated in the MPIO management station 116, and responsive to receipt of the additional command, to at least partially reverse the reduction in the rate at which additional ones of the IO operations are sent from the host device 102-1 to the storage array 105. An example of such an additional command is referred to herein as a “resume previous rate” command.

Although described in the context of some embodiments as being performed by the MPIO driver 112-1 utilizing its path selection logic 114-1 and IO throttling logic 115-1, one or more of the above-described operations in other embodiments can be performed elsewhere within the host device 102-1. Also, other ones of the MPIO drivers 112 and their respective other host devices 102 can be similarly configured.

An example of a process including operations of the type outlined above will be described below in conjunction with the flow diagram of FIG. 2. These and other operations referred to herein as being performed by one or more host devices operating in conjunction with one or more storage arrays of a storage system can in other embodiments involve additional or alternative system components, possibly including one or more external servers such as MPIO management station 116.

As indicated previously, the initiators of the initiator-target pairs illustratively comprise respective HBAs of the host device 102-1 and the targets of the initiator-target pairs comprise respective storage array ports of the storage array 105.

Negotiated rates of the respective particular initiator and the corresponding target illustratively comprise respective negotiated data rates determined by execution of at least one link negotiation protocol for an associated one of the paths.

In some embodiments, at least a portion of the initiators comprise virtual initiators, such as, for example, respective ones of a plurality of N-Port ID Virtualization (NPIV) initiators associated with one or more Fibre Channel (FC) network connections. Such initiators illustratively utilize NVMe arrangements such as NVMe/FC, although other protocols can be used. Other embodiments can utilize other types of virtual initiators in which multiple network addresses can be supported by a single network interface, such as, for example, multiple media access control (MAC) addresses on a single network interface of an Ethernet network interface card (NIC). Accordingly, in some embodiments, the multiple virtual initiators are identified by respective ones of a plurality of media MAC addresses of a single network interface of a NIC. Such initiators illustratively utilize NVMe arrangements such as NVMe/TCP, although again other protocols can be used.

In some embodiments, the NPIV feature of FC allows a single host HBA port to expose multiple World Wide Numbers (WWNs) to the SAN 104 and the storage array 105. A WWN or World Wide Identifier (WWID) is a unique identifier used in various types of storage technologies that may be implemented in illustrative embodiments herein, including, for example, SCSI, NVMe, FC, Parallel Advanced Technology Attachment (PATA), Serial Advanced Technology Attachment (SATA), Serial Attached SCSI (SAS) and others, and may be viewed as an example of what is more generally referred to herein as a virtual identifier. The NPIV feature is used, for example, when there are multiple IO producers on a given host device with a need to distinguish which IO is related to which producer.

One such case is a system involving virtual machines (VMs), where multiple VMs run on a single ESXi server with HBAs. All VMs are using all HBAs but there is a need to be able to distinguish which IO belongs to which VM, for example, in order to implement service level objectives (SLOs) between the various VMs, illustratively at an OS level. Each of the NPIV initiators behaves as if it is a “normal” or physical initiator, in that it logs into a storage array port, requires masking, etc. Another example of NPIV usage is in the context of AIX servers, where different logical partitions each use a different NPIV initiator over the same host HBA port.

Accordingly, in some embodiments, the multiple virtual initiators are associated with a single HBA of the host device 102-1 but have respective unique identifiers associated therewith.

Additionally or alternatively, different ones of the multiple virtual initiators are illustratively associated with respective different ones of a plurality of virtual machines of the host device that share a single HBA of the host device, or a plurality of logical partitions of the host device that share a single HBA of the host device.

Again, numerous alternative virtual initiator arrangements are possible, as will be apparent to those skilled in the art. The term “virtual initiator” as used herein is therefore intended to be broadly construed. It is also to be appreciated that other embodiments need not utilize any virtual initiators. References herein to the term “initiators” are intended to be broadly construed, and should therefore be understood to encompass physical initiators, virtual initiators, or combinations of both physical and virtual initiators.

These and other aspects of detection and mitigation of slow drain issues are illustratively performed by each of the instances of IO throttling logic 115 in respective ones of the MPIO drivers 112 of the multi-path layer, possibly operating in conjunction with their corresponding instances of path selection logic 114. However, it is to be appreciated that additional system components such as MPIO management station 116 participate in the disclosed functionality for detection and mitigation of slow drain issues in illustrative embodiments. The term “slow drain issue” as used herein is intended to be broadly construed, so as to encompass a wide variety of additional or alternative congestion-related conditions that can adversely impact the performance of a storage system.

These and other illustrative embodiments disclosed herein provide functionality for detection and mitigation of slow drain issues, with at least portions of that functionality being implemented using one or more MPIO drivers of a multi-path layer of at least one host device. The MPIO drivers can comprise PowerPath® drivers suitably modified to implement the techniques disclosed herein. Other types of host multi-pathing software from other vendors can be similarly modified to implement the techniques disclosed herein. Again, MPIO drivers are not required, and other types of host drivers or more generally other host device components can be used.

As described above, in illustrative embodiments disclosed herein, the host devices 102 are configured to interact with storage array 105 to provide detection and mitigation of slow drain issues between host devices 102 and storage array 105.

An example of an algorithm performed by a given one of the host devices 102-1 utilizing its MPIO driver 112-1 and its corresponding instances of path selection logic 114-1 and IO throttling logic 115-1 will now be described. In the following description, a host device is also referred to herein as simply a “host.” Similarly, a storage array is also referred to herein as simply an “array.”

By way of example, a slow drain issue can arise in a storage environment when a link rate negotiated between an HBA or other initiator of a host and a switch of the SAN 104 is mismatched with a corresponding link rate negotiated between a target port of the array and the switch of the SAN 104, and more particularly, when the host negotiated rate is lower than the array negotiated rate. This type of slow drain issue generally presents itself in the context of read commands, where the host sends read requests for certain payloads. The array retrieves the requested data from the appropriate storage device(s) and sends it to the host. However, if the array negotiated rate is higher than the host negotiated rate, the array will send the data to the switch of the SAN 104 faster than the host can read the data from the switch, and a backlog of data from the array will accumulate in the switch.

This backlog will consume switch IO buffers typically used for temporary storage of data in the event of short-term minor speed gradients. When the switch lacks sufficient available IO buffers, all communication slows down considerably.

The slow drain issue typically does not manifest itself in write commands. This is generally due to various flow control mechanisms that are commonly performed in conjunction with write commands, such as those implemented utilizing TRANSFER_RDY messages of standard storage access protocols.

Slow drain issues can arise in other contexts as well, such as when a new storage array is introduced into an existing storage environment (e.g., via seamless migration), where the newer array supports higher port speeds than the previous array. In this context, the slow drain issue can arise as soon as the host switches to the new array. Slow drain issues can also occur when an array port goes bad and is replaced by new array port hardware that supports a higher communication speed.

Slow drain is also a very common problem in FC networks. As indicated above, slow drain occurs in some embodiments when a host starts demanding more data than it can consume from the array. This can occur when the initiators of the host, illustratively implemented as respective HBAs of the host, are of lower speed than the storage array target ports. Here, the term “speed” illustratively refers to a negotiated transmission rate of the initiator or target.

For example, assume the host HBA speed is at 8 GB/sec and the storage array target port speed is at 16 GB/s, and the host starts asking for read IOs at a speed of more than 8 GB/sec. This results in IOs starting to be queued up in the switch fabric of the SAN 104. IO backlogs start getting built up from the switch port and also start getting built up in the inter-switch links (ISLs). Slowly the switch fabric starts getting congested and other hosts connected to the same fabric start experiencing IO delays as there is congestion in the switch fabric. The IO performance of these other hosts starts deteriorating and the entire switch fabric becomes congested.

Hosts which are running IOs generally do not know the reason for the congestion in the switch fabric, and all such hosts start to see a drop in IO processing performance. Congestion spreading of this type can occur due a slow drain issue involving a relatively small number of logical storage devices and associated paths.

It is assumed for purposes of the following algorithm description that host multi-pathing software is utilized to implement techniques for slow drain detection and mitigation. Such host multi-pathing software illustratively operates in cooperation with a PPMA that is in communication with each of the host devices 102 and with the storage array 105, although it is to be understood that other types of intermediary devices can be used in place of the PPMA in other embodiments.

For example, the PPMA illustratively obtains host initiator speed from a host device 102-1 via OS native CLI of the host device 102-1. For example, the host device 102-1 can obtain such information via the OS native CLI and send it to the PPMA responsive to a request from the PPMA, although other techniques could be used. The PPMA may be installed in a data center or other location within an information processing system to monitor the host devices 102 and their respective MPIO drivers 112. The PPMA illustratively obtains the storage array port speed using a REST call to the storage array, although again other techniques can be used. The PPMA now has both the host initiator and array target port speeds, for each of multiple host initiators and multiple array target ports.

The example algorithm illustratively includes the following steps:

1. The MPIO driver 112-1 monitors response times of read IO operations to determine if one or more of the response times of the read IO operations cross a specified threshold, illustratively set by an administrator or other user. Assume the threshold is X milliseconds (ms). The value of X will likely vary depending upon implementation-specific factors, but may be on the order of 10 to 100 milliseconds, although other values can be used.

2. The MPIO driver 112-1 continues its monitoring of the response times of the read IO operations, and if the response times of the read IO operations remain above the specified threshold for at least Y seconds after an initial crossing of the X-value threshold, an alert is generated and sent to the PPMA. The value of Y will also likely vary depending upon implementation-specific factors, but may be on the order of 1 to 10 seconds, although other values can be used. The values X and Y collectively provide an example of a multi-dimensional threshold, although single-dimensional thresholds can also be used. These and other thresholds in some embodiments are determined using machine learning or other techniques based on previously-stored historical response times, and the response times are illustratively measured on at least one of a per-path basis and a per-device basis. Accordingly, the MPIO driver 112-1 can measure response times separately for read IO operations sent over each of a plurality of paths and directed to each of a plurality of logical storage devices.

3. The PPMA receives the alert from the host and looks for similar alerts from other hosts connected to same switch fabric of the SAN 104.

4. If the PPMA also receives these alerts from one or more other hosts, this tends to indicate that there is a slow drain issue in the SAN 104.

5. As the PPMA already has the host initiator and storage array target port speeds, it will send a throttling command to the host which has the most significant mismatch in initiator-target speeds, of the various hosts that share the switch fabric of the SAN 104. Assume this is the host 102-1, although it could be any of the hosts. The throttling command illustratively directs the host 102-1 to slow down to the rate of at least one of the host initiators. For example, if the speed of the HBA exhibiting the greatest mismatch is 8 GB/sec, then the MPIO driver 112-1 will start throttling the IOs for that HBA to 8 GB/sec.

6. Once the host which had the greatest mismatch starts throttling, there should be an improvement in congestion in the SAN 104 as the slow drain issue is alleviated.

7. The PPMA keeps checking for any more alerts from the hosts. If it sees no more alerts from the particular host it previously commanded to throttle its IOs, for at least a specified time period, it sends another command to that host to direct it to stop throttling its IOs as the congestion issue has been mitigated.

It is to be appreciated that the particular steps of the algorithm described above are presented by way of illustrative example only, and additional or alternative steps can be used in other embodiments. Also, the order of the steps can be varied, and/or at least some of the steps can be performed at least in part in parallel with one another.

This example algorithm advantageously avoids the need to alter the host and storage array software to process enhanced congestion notifications received from next-generation switch fabrics, and/or to upgrade the system to the next-generation switch fabrics in the first place.

In addition, this example algorithm avoids the need to a storage administrator or other user to detect the slow drain problem and login to a storage array graphical user interface (GUI) to set a host bandwidth limit in the storage array.

In other embodiments, similar techniques can be implemented using the multi-pathing software of the hosts, possibly without utilizing the PPMA. Accordingly, some embodiments do not necessarily include a PPMA. Other types of management servers or other intermediary devices can be used in addition to or in place of a PPMA.

These and other illustrative embodiments provide significant advantages over conventional practice. For example, such embodiments are much more efficient and effective than conventional approaches that swap hardware or manually use array resources to tell the array to lower its bandwidth when communicating with the specific slower initiator.

Illustrative embodiments can be implemented, for example, in one or more MPIO drivers of one or more host devices, with such MPIO drivers collectively providing a multi-path layer of the host devices.

For example, some embodiments are implemented though modification of otherwise conventional multi-pathing software, such as PowerPath® drivers commercially available from Dell Technologies. Other embodiments can be implemented in other MPIO drivers from other multi-pathing software vendors.

In some embodiments, an MPIO driver can become aware of a slow drain issue by communicating with an array that exports information specifying negotiated speed of its ports. The MPIO driver can get the host negotiated speed either from the host OS itself, or from an array that also detected the host negotiated speed and exported it to the MPIO driver (depending on the level of array support for exporting negotiated speeds).

In some embodiments, the MPIO driver is aware of the host negotiated speed and the array port negotiated speed for each path corresponding to an initiator-target pair, where the initiator is illustratively an HBA of the host and the target is a particular port of the array.

Moreover, other host device components, such as logic instances and/or host processors, can additionally or alternatively be used, with or without a PPMA or other similar central server or intermediary device.

Illustrative embodiments disclosed herein can provide detection and mitigation of slow drain issues for a wide variety of different types of host devices, such as host devices comprising ESXi servers or AIX servers.

Portions of the above-described algorithms and other related techniques and functionality are illustratively implemented by a given MPIO driver on a corresponding host device, and similarly by other MPIO drivers on respective other host devices. Such MPIO drivers illustratively form a multi-path layer or MPIO layer comprising multi-pathing software of the host devices. Other types of multi-pathing software and host drivers can be used in other embodiments. Additionally or alternatively, other host device components can be used to implement at least portions of the disclosed functionality for detection and mitigation of slow drain issues.

Although VU commands are used in illustrative embodiments herein, other types of commands can be used in other embodiments. For example, various types of log sense, mode sense and/or other “read-like” commands, possibly including one or more commands of a standard storage access protocol such as the above-noted SCSI and NVMe access protocols, can be used in other embodiments.

Additional examples of arrangements for detection and mitigation of slow drain issues will be described elsewhere herein in conjunction with the embodiments of FIGS. 2 through 5. Other types of arrangements for detection and mitigation of slow drain issues can be used in other embodiments.

These and other functions related to detection and mitigation of slow drain issues that are referred to herein as being performed by or under the control of the MPIO drivers 112 through interaction with the storage array 105 can in some embodiments be performed at least in part outside of MPIO drivers 112 utilizing other system components.

The above-described functions associated with detection and mitigation of slow drain issues in the MPIO driver 112-1 in some embodiments are carried out at least in part under the control of its IO throttling logic 115-1, illustratively operating in cooperation with path selection logic 114-1. For example, the IO throttling logic 115-1 is illustratively configured to control performance of portions of an algorithm comprising the steps of the process in the flow diagram to be described below in conjunction with FIG. 2. In other embodiments, one or more such steps can be more generally performed by the host device 102-1.

It is assumed that each of the other MPIO drivers 112 is configured in a manner similar to that described above and elsewhere herein for the first MPIO driver 112-1. The other host devices 102 of the system 100 are therefore also configured to communicate over the SAN 104 with the storage array 105. The MPIO drivers 112 of such other host devices are each similarly configured to deliver IO operations from its corresponding one of the sets of IO queues 110 to the storage array 105 over selected paths through the SAN 104, and to perform the disclosed functionality for detection and mitigation of slow drain issues.

Accordingly, functionality described above in the context of the first MPIO driver 112-1 and the first host device 102-1 is assumed to be similarly performed by each of the other MPIO drivers 112 and/or more generally by their respective host devices 102.

The MPIO drivers 112 may be otherwise configured utilizing well-known MPIO functionality such as that described in K. Piepho, “Dell EMC SC Series Storage: Microsoft Multipath I/O,” Dell EMC Engineering, June 2017, which is incorporated by reference herein. Such conventional MPIO functionality is suitably modified in illustrative embodiments disclosed herein to support detection and mitigation of slow drain issues.

Although in some embodiments certain commands used by the host devices 102 to communicate with the storage array 105 illustratively comprise SCSI commands, other types of commands and command formats can be used in other embodiments. For example, some embodiments can implement IO operations utilizing command features and functionality associated with NVMe, as described in the NVMe Specification, Revision 1.3, May 2017, which is incorporated by reference herein. Other NVMe storage access protocols of this type that may be utilized in illustrative embodiments disclosed herein include NVMe/FC, NVMeF and NVMe/TCP.

The storage array 105 in the present embodiment is assumed to comprise a persistent memory that is implemented using a flash memory or other type of non-volatile memory of the storage array 105. More particular examples include NAND-based flash memory or other types of non-volatile memory such as resistive RAM, phase change memory, spin torque transfer magneto-resistive RAM (STT-MRAM) and Intel Optane™ devices based on 3D XPoint™ memory. The persistent memory is further assumed to be separate from the storage devices 106 of the storage array 105, although in other embodiments the persistent memory may be implemented as a designated portion or portions of one or more of the storage devices 106. For example, in some embodiments the storage devices 106 may comprise flash-based storage devices, as in embodiments involving all-flash storage arrays, or may be implemented in whole or in part using other types of non-volatile memory.

The storage array 105 in the present embodiment may comprise additional components not explicitly shown in the figure, such as a response time control module and IO operation priority queues, illustratively configured to make use of the above-described persistent memory. For example, the response time control module may be used to implement storage array based adjustments in response time for particular IO operations based at least in part on service level objective (SLO) information stored by the storage array 105 in its persistent memory. The response time control module is assumed to operate in conjunction with the above-noted IO operation priority queues.

The storage array 105 illustratively utilizes its IO operation priority queues to provide different levels of performance for IO operations. For example, the IO operation priority queues may have respective different priority levels. The storage array 105 may be configured to provide different priority levels for different ones of the IO operations by assigning different ones of the IO operations to different ones of the IO operation priority queues. The IO operation priority queues are illustratively associated with respective SLOs for processing of IO operations in the storage array 105. Process tags may be used in assigning different ones of the IO operations to different ones of the IO operation priority queues, as disclosed in U.S. Pat. No. 10,474,367, entitled “Storage System with Input-Output Performance Control Utilizing Application Process Detection,” which is incorporated by reference herein.

As mentioned above, communications between the host devices 102 and the storage array 105 may utilize PCIe connections or other types of connections implemented over one or more networks, using interfaces and protocols as previously described. Numerous other interfaces and associated protocols can be used in other embodiments.

The storage array 105 in some embodiments may be implemented as part of cloud infrastructure in the form of a cloud-based system such as an Amazon Web Services (AWS) system. Other examples of cloud-based systems that can be used to provide at least portions of the storage array 105 and possibly other portions of system 100 include Google Cloud Platform (GCP) and Microsoft Azure.

The storage devices 106 of the storage array 105 can be implemented using solid state drives (SSDs). Such SSDs are implemented using non-volatile memory (NVM) devices such as flash memory. Other types of NVM devices that can be used to implement at least a portion of the storage devices 106 include non-volatile random access memory (NVRAM), phase-change RAM (PC-RAM) and magnetic RAM (MRAM). These and various combinations of multiple different types of NVM devices or other storage devices may also be used. For example, hard disk drives (HDDs) can be used in combination with or in place of SSDs or other types of NVM devices. Accordingly, numerous other types of electronic or magnetic media can be used in implementing at least a subset of the storage devices 106.

The storage array 105 may additionally or alternatively be configured to implement multiple distinct storage tiers of a multi-tier storage system. By way of example, a given multi-tier storage system may comprise a fast tier or performance tier implemented using flash storage devices or other types of SSDs, and a capacity tier implemented using HDDs, possibly with one or more such tiers being server based. A wide variety of other types of storage devices and multi-tier storage systems can be used in other embodiments, as will be apparent to those skilled in the art. The particular storage devices used in a given storage tier may be varied depending on the particular needs of a given embodiment, and multiple distinct storage device types may be used within a single storage tier. As indicated previously, the term “storage device” as used herein is intended to be broadly construed, and so may encompass, for example, SSDs, HDDs, flash drives, hybrid drives or other types of storage products and devices, or portions thereof, and illustratively include logical storage devices such as LUNs.

As another example, the storage array 105 may be used to implement one or more storage nodes in a cluster storage system comprising a plurality of storage nodes interconnected by one or more networks.

It should therefore be apparent that the term “storage array” as used herein is intended to be broadly construed, and may encompass multiple distinct instances of a commercially-available storage array. For example, the storage array 105 may comprise one or more storage arrays such as one or more Unity™ or PowerMax™ storage arrays, commercially available from Dell Technologies.

Other types of storage products that can be used in implementing a given storage system in illustrative embodiments include software-defined storage, cloud storage, object-based storage and scale-out storage. Combinations of multiple ones of these and other storage types can also be used in implementing a given storage system in an illustrative embodiment.

In some embodiments, a storage system comprises first and second storage arrays arranged in an active-active configuration. For example, such an arrangement can be used to ensure that data stored in one of the storage arrays is replicated to the other one of the storage arrays utilizing a synchronous replication process. Such data replication across the multiple storage arrays can be used to facilitate failure recovery in the system 100. One of the storage arrays may therefore operate as a production storage array relative to the other storage array which operates as a backup or recovery storage array.

It is to be appreciated, however, that embodiments disclosed herein are not limited to active-active configurations or any other particular storage system arrangements. Accordingly, illustrative embodiments herein can be configured using a wide variety of other arrangements, including, by way of example, active-passive arrangements, active-active Asymmetric Logical Unit Access (ALUA) arrangements, and other types of ALUA arrangements.

These and other storage systems can be part of what is more generally referred to herein as a processing platform comprising one or more processing devices each comprising a processor coupled to a memory. A given such processing device may correspond to one or more virtual machines or other types of virtualization infrastructure such as Docker containers or other types of LXCs. As indicated above, communications between such elements of system 100 may take place over one or more networks.

The term “processing platform” as used herein is intended to be broadly construed so as to encompass, by way of illustration and without limitation, multiple sets of processing devices and one or more associated storage systems that are configured to communicate over one or more networks. For example, distributed implementations of the host devices 102 are possible, in which certain ones of the host devices 102 reside in one data center in a first geographic location while other ones of the host devices 102 reside in one or more other data centers in one or more other geographic locations that are potentially remote from the first geographic location. Thus, it is possible in some implementations of the system 100 for different ones of the host devices 102 to reside in different data centers than the storage array 105.

Numerous other distributed implementations of the host devices 102 and/or the storage array 105 are possible. Accordingly, the storage array 105 can also be implemented in a distributed manner across multiple data centers.

It is to be appreciated that these and other features of illustrative embodiments are presented by way of example only, and should not be construed as limiting in any way. Accordingly, different numbers, types and arrangements of system components such as host devices 102, SAN 104, storage array 105, storage devices 106, sets of IO queues 110, and MPIO drivers 112, including their corresponding instances of path selection logic 114 and IO throttling logic 115, can be used in other embodiments.

It should also be understood that the particular sets of modules and other components implemented in the system 100 as illustrated in FIG. 1 are presented by way of example only. In other embodiments, only subsets of these components, or additional or alternative sets of components, may be used, and such components may exhibit alternative functionality and configurations.

The operation of the information processing system 100 will now be described in further detail with reference to the flow diagram of the illustrative embodiment of FIG. 2. The process as shown includes steps 200 through 212, and is suitable for use in the system 100 but is more generally applicable to other types of systems comprising at least one host device and a storage system. The storage system in this embodiment is assumed to comprise at least one storage array having a plurality of storage devices. The storage devices can include logical storage devices such as LUNs or other logical storage volumes.

The steps of the FIG. 2 process are illustratively performed at least in part by or under the control of a multi-path layer comprising one or more MPIO drivers of respective host devices, a storage array or other storage system, and one or more additional components such as an external server comprising an MPIO management station. Other arrangements of additional or alternative system components can be configured to perform at least portions of one or more of the steps of the FIG. 2 process in other embodiments.

The steps shown in FIG. 2 more specifically relate to processing performed by a given host device, also referred to in the following description as simply a “host,” interacting with a storage array and an MPIO management station. It is assumed that similar processes are implemented for each of a plurality of additional hosts that interact with the storage array and the MPIO management station.

In step 200, an MPIO driver on a host monitors response times for the IO operations that it sends from the host to a storage array over selected paths from initiators of the host to respective targets of the storage array. For example, the MPIO driver of the host illustratively obtains an IO operation from an application executing on the host and sends the IO operation from the host to the storage array over a selected path. It is assumed in the present embodiment that the MPIO driver of the host device delivers IO operations, such as read requests and write requests in the form of corresponding storage access protocol commands, from the host device to the storage array over selected paths through a SAN.

In step 202, a determination is made by the MPIO driver as to whether or not the response times for at least a subset of the IO operations are above a designated threshold for at least a specified monitoring time period. Responsive to an affirmative determination, the process moves to step 204, and otherwise returns to step 200 as indicated.

In step 204, the MPIO driver sends an alert to an MPIO management station, which is coupled to the host and to the storage array. Other types of servers, computers, appliances or other intermediary devices can be used in place of the MPIO management station in other embodiments.

In step 206, the MPIO driver receives a throttling command from the MPIO management station. The throttling command illustratively directs the MPIO driver to reduce a rate at which it sends IO operations over at least one of the paths between the host and the storage array. For example, the throttling command may direct the MPIO driver to reduce the rate at which it sends IO operations over a particular path associated with a greatest amount of initiator-target negotiated rate mismatch detected by the MPIO management station. As another example, the throttling command may direct the MPIO driver to reduce the rate at which it sends IO operations over multiple paths each associated with a relatively high amount of initiator-target negotiated rate mismatch detected by the MPIO management station, as compared to other paths associated with a relatively low amount of initiator-target negotiated rate mismatch. A wide variety of other types of throttling commands can be used.

In step 208, the MPIO driver sends IO operations at a reduced rate over one or more of the paths in accordance with the throttling command received from the MPIO management station.

In step 210, a determination is made by the MPIO driver as to whether or not an additional command, illustratively a “resume previous rate” command, has been received by the MPIO driver from the MPIO management station. Responsive to an affirmative determination, the process moves to step 212, and otherwise returns to step 208 as indicated.

In step 212, the MPIO driver resumes the rate that it used previous to receipt of the throttling command, for sending IOs over the one or more paths. The process then returns to step 200 to continue to monitor response times as described above.

The particular processing operations and other system functionality described in conjunction with the flow diagram of FIG. 2 are presented by way of illustrative example only, and should not be construed as limiting the scope of the disclosure in any way. Alternative embodiments can use other types of processing operations involving host devices, storage systems and functionality for detection and mitigation of slow drain issues. For example, the ordering of the process steps may be varied in other embodiments, or certain steps may be performed at least in part concurrently with one another rather than serially. Also, one or more of the process steps may be repeated periodically, or multiple instances of the process can be performed in parallel with one another in order to implement a plurality of different arrangements for detection and mitigation of slow drain issues within a given information processing system.

Functionality such as that described in conjunction with the flow diagram of FIG. 2 can be implemented at least in part in the form of one or more software programs stored in memory and executed by a processor of a processing device such as a computer or server. As will be described below, a memory or other storage device having executable program code of one or more software programs embodied therein is an example of what is more generally referred to herein as a “processor-readable storage medium.”

Referring now to FIG. 3, another illustrative embodiment is shown. In this embodiment, an information processing system 300 comprises host-side elements that include application processes 311, path selection logic 314 and IO throttling logic 315, and storage-side elements that include MPIO management station interface logic 321 and one or more target port data structures 322 for storing negotiated rate information for respective target ports of at least one storage array. There may be separate instances of one or more such elements associated with each of a plurality of storage arrays of the system 300.

The system 300 is configured in accordance with a layered system architecture that illustratively includes a host device processor layer 330, an MPIO layer 332, an HBA layer 334, a switch fabric layer 336, a storage array port layer 338 and a storage array processor layer 340. The host device processor layer 330, the MPIO layer 332 and the HBA layer 334 are associated with one or more host devices, the switch fabric layer 336 is associated with one or more SANs or other types of networks, and the storage array port layer 338 and storage array processor layer 340 are associated with one or more storage arrays (“SAs”). The storage array processors of the storage array processor layer 340 may be viewed as corresponding to one or more storage controllers such as the storage controllers 120 of the storage array 105.

The application processes 311 of the host device processor layer 330 generate IO operations that are processed by the MPIO layer 332 for delivery to the one or more storage arrays over the SAN comprising switch fabrics of switch fabric layer 332, using detection and mitigation of slow drain issues as disclosed herein. Paths are determined by the path selection logic 314 for sending such IO operations to the one or more storage arrays.

The MPIO layer 332 is an example of what is also referred to herein as a multi-path layer, and comprises one or more MPIO drivers implemented in respective host devices. Each such MPIO driver illustratively comprises respective instances of path selection logic 314 and IO throttling logic 315 configured as previously described. Additional or alternative layers and logic arrangements can be used in other embodiments.

In a manner similar to that described elsewhere herein, the MPIO layer 332 comprising IO throttling logic 315 illustratively processes a plurality of IO operations generated by a given host device. The IO operations are sent by the MPIO layer 332 to a storage array over respective paths selected using one or more algorithms implemented by path selection logic 314.

In the system 300, path selection logic 314 is configured to select different paths for sending IO operations from a given host device to a storage array. These paths as illustrated in the figure include a first path from a particular HBA denoted HBA1 through a particular switch fabric denoted SF1 to a particular storage array port denoted PORT1, and a second path from another particular HBA denoted HBA2 through another particular switch fabric denoted SF2 to another particular storage array port denoted PORT2.

These two particular paths are shown by way of illustrative example only, and in many practical implementations there will typically be a much larger number of paths between the one or more host devices and the one or more storage arrays, depending upon the specific system configuration and its deployed numbers of HBAs, switch fabrics and storage array ports. For example, each host device in the FIG. 3 embodiment can illustratively have a set of k paths to a shared storage array, or alternatively different ones of the host devices can have different numbers and types of paths to the storage array.

The path selection logic 314 of the MPIO layer 332 in this embodiment selects paths for delivery of IO operations to the one or more storage arrays having the storage array ports of the storage array port layer 338. More particularly, the path selection logic 314 determines appropriate paths over which to send particular IO operations to particular logical storage devices of the one or more storage arrays.

In an example process for detection and mitigation of slow drain issues in the system 300, an MPIO driver of the MPIO layer 332 monitors response times of IO operations sent to one or more storage arrays over particular paths. Responsive to IO operation response times being above a threshold for at least a specified monitoring time period for one or more HBAs or other initiators of its corresponding host device, the MPIO driver generates an alert and sends it to an MPIO management station, associated with the MPIO layer 332 but not explicitly shown in this figure. The MPIO management station illustratively obtains negotiated rate information for each of multiple HBAs or other initiators of multiple host devices, and obtains negotiated rate information for each of multiple target ports or other targets of one or more storage arrays. The MPIO management station receives alerts of the type described above, from MPIO drivers of one or more of the host devices, and uses those alerts and the negotiated rate information to determine which of the host devices is currently experiencing the greatest amount of initiator-threshold mismatch among the paths for which alerts were received. The MPIO management station then sends a throttling command to the MPIO drivers of one or more of the host devices that are currently experiencing the greatest amount of initiator-threshold mismatch among the paths for which alerts were received, so as to mitigate the slow drain issue. The MPIO management station subsequently reverses the throttling command by sending a “resume previous rate” or other additional command after the slow drain issue has been mitigated.

Some implementations of the system 300 can include a relatively large number of host devices (e.g., 1000 or more host devices), although as indicated previously different numbers of host devices, and possibly only a single host device, may be present in other embodiments. Each of the host devices is typically allocated with a sufficient number of HBAs to accommodate predicted performance needs. In some cases, the number of HBAs per host device is on the order of 4, 8 or 16 HBAs, although other numbers of HBAs could be allocated to each host device depending upon the predicted performance needs. A typical storage array may include on the order of 128 ports, although again other numbers can be used based on the particular needs of the implementation. The number of host devices per storage array port in some cases can be on the order of 10 host devices per port. The HBAs of the host devices are assumed to be zoned and masked to the storage array ports in accordance with the predicted performance needs, including user load predictions.

A given host device of system 300 can be configured to initiate an automated path discovery process to discover new paths responsive to updated zoning and masking or other types of storage system reconfigurations performed by a storage administrator or other user. For certain types of host devices, such as host devices using particular operating systems such as Windows, ESX or Linux, automated path discovery via the MPIO drivers of a multi-path layer is typically supported. Other types of host devices using other operating systems such as AIX in some implementations do not necessarily support such automated path discovery, in which case alternative techniques can be used to discover paths.

Referring now to FIG. 4, an example data structure 400 utilized in providing detection and mitigation of slow drain issues as disclosed herein is shown.

In the example data structure 400, which may be viewed as one of the target port data structures 122 of the FIG. 1 embodiment or one of the target port data structures 322 of the FIG. 3 embodiment, a storage array stores target port information, illustratively negotiated rate information for each of a plurality of storage array ports denoted by port identifiers Port ID 1, Port ID 2, . . . Port ID L.

At least portions of the negotiated rate information stored in the data structure 400 are illustratively provided by the storage array to an external server such as such as the MPIO management station 116, possibly in response to a query received from the MPIO management station 116 or other external server. Such an “external server” may be, for example, a central server, and is illustratively external to at least one storage array, and possible also external to one or more host devices.

The particular data structure arrangement shown in FIG. 4 is only an example, and numerous other types and arrangements of data structures can be utilized in other embodiments.

Referring now to FIG. 5, an information processing system 500 in another illustrative embodiment comprises a plurality of host devices 502, individually denoted as host devices 502-1, host device 502-2, host device 502-3, . . . host device 502-N. The system 500 further comprises a storage array 505, and an MPIO management station 516. It is assumed that each of the host devices 502 is in communication with the storage array 505 and the MPIO management station 516. In a process for detection and mitigation of slow drain issues in the system 500, the MPIO management station illustratively obtains negotiated rate information for each of multiple HBAs or other initiators of the host devices 502, and obtains negotiated rate information for each of multiple target ports or other targets of the storage array 505. In addition, the MPIO management station receives alerts from one or more of the host devices 502 regarding IO operation response times being above a threshold for at least a specified monitoring time period for one or more HBAs or other initiators of each such host device, and uses those alerts to determine which of the host devices 502 is currently experiencing the greatest amount of initiator-threshold mismatch among the paths for which alerts were received. The MPIO management station 516 then sends a throttling command to one or more of the host devices 502 that are currently experiencing the greatest amount of initiator-threshold mismatch among the paths for which alerts were received, so as to mitigate the slow drain issue. The MPIO management station 516 reverses the throttling command by sending a “resume previous rate” or other additional command after the slow drain issue has been mitigated.

The above-described processes, algorithms and other features and functionality disclosed herein are presented by way of illustrative example only, and other embodiments can utilize additional or alternative arrangements. For example, other types of intermediary devices can be used in place of the MPIO management station 516, such as various alternative arrangements of servers, appliances and/or computers.

Also, as mentioned previously, different instances of the above-described processes, algorithms and other techniques for detection and mitigation of slow drain issues can be performed using different system components. For example, various aspects of functionality for detection and mitigation of slow drain issues in some embodiments can be implemented at least in part using one or more servers that are external to a storage array 105 or other type of storage system. Also, processing logic can be implemented using other types of host drivers, such as, for example, iSCSI drivers, or more generally other host device components.

The particular arrangements described above for detection and mitigation of slow drain issues are therefore presented by way of illustrative example only. Numerous alternative arrangements of these and other features can be used in implementing the detection and mitigation of slow drain issues in other illustrative embodiments.

The illustrative embodiments disclosed herein can provide a number of significant advantages relative to conventional arrangements.

For example, some embodiments are advantageously configured to provide highly efficient and effective detection and mitigation of slow drain issues between host devices and a storage array or other storage system.

These embodiments avoid the disadvantages of conventional techniques such as swapping hardware or manually using array resources to tell the array to lower its bandwidth when communicating with a specific slower initiator.

Some embodiments therefore avoid the need for a storage administrator or other user to detect the slow drain problem and login to a storage array GUI to set a host bandwidth limit in the storage array.

Additionally or alternatively, illustrative embodiments can avoid the need to alter the host and storage array software to process enhanced congestion notifications received from next-generation switch fabrics, and/or to upgrade the system to the next-generation switch fabrics in the first place.

Various aspects of functionality associated with detection and mitigation of slow drain issues as disclosed herein can be implemented in a storage system, in a host device, or partially in a storage system and partially in a host device, and additionally or alternatively using other arrangements of one or more processing devices each comprising at least a processor and a memory coupled to the processor.

It is to be appreciated that the particular advantages described above and elsewhere herein are associated with particular illustrative embodiments and need not be present in other embodiments. Also, the particular types of information processing system features and functionality as illustrated in the drawings and described above are exemplary only, and numerous other arrangements may be used in other embodiments.

It was noted above that portions of an information processing system as disclosed herein may be implemented using one or more processing platforms. Illustrative embodiments of such platforms will now be described in greater detail. These and other processing platforms may be used to implement at least portions of other information processing systems in other embodiments. A given such processing platform comprises at least one processing device comprising a processor coupled to a memory.

One illustrative embodiment of a processing platform that may be used to implement at least a portion of an information processing system comprises cloud infrastructure including virtual machines implemented using a hypervisor that runs on physical infrastructure. The cloud infrastructure further comprises sets of applications running on respective ones of the virtual machines under the control of the hypervisor. It is also possible to use multiple hypervisors each providing a set of virtual machines using at least one underlying physical machine. Different sets of virtual machines provided by one or more hypervisors may be utilized in configuring multiple instances of various components of the system.

These and other types of cloud infrastructure can be used to provide what is also referred to herein as a multi-tenant environment. One or more system components such as virtual machines, or portions thereof, are illustratively implemented for use by tenants of such a multi-tenant environment.

Cloud infrastructure as disclosed herein can include cloud-based systems such as Amazon Web Services, Google Cloud Platform and Microsoft Azure. Virtual machines provided in such systems can be used to implement a fast tier or other front-end tier of a multi-tier storage system in illustrative embodiments. A capacity tier or other back-end tier of such a multi-tier storage system can be implemented using one or more object stores such as Amazon S3, Google Cloud Platform Cloud Storage, and Microsoft Azure Blob Storage.

In some embodiments, the cloud infrastructure additionally or alternatively comprises a plurality of containers illustratively implemented using respective operating system kernel control groups of one or more container host devices. For example, a given container of cloud infrastructure illustratively comprises a Docker container or other type of LXC implemented using a kernel control group. The containers may run on virtual machines in a multi-tenant environment, although other arrangements are possible. The containers may be utilized to implement a variety of different types of functionality within the system 100. For example, containers can be used to implement respective compute nodes or storage nodes of a cloud-based system. Again, containers may be used in combination with other virtualization infrastructure such as virtual machines implemented using a hypervisor.

Another illustrative embodiment of a processing platform that may be used to implement at least a portion of an information processing system comprises a plurality of processing devices which communicate with one another over at least one network. The network may comprise any type of network, including by way of example a global computer network such as the Internet, a WAN, a LAN, a satellite network, a telephone or cable network, a cellular network, a wireless network such as a WiFi or WiMAX network, or various portions or combinations of these and other types of networks.

Each processing device of the processing platform comprises a processor coupled to a memory. The processor may comprise a microprocessor, a microcontroller, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a graphics processing unit (GPU) or other type of processing circuitry, as well as portions or combinations of such circuitry elements. The memory may comprise random access memory (RAM), read-only memory (ROM), flash memory or other types of memory, in any combination. The memory and other memories disclosed herein should be viewed as illustrative examples of what are more generally referred to as “processor-readable storage media” storing executable program code of one or more software programs.

Articles of manufacture comprising such processor-readable storage media are considered illustrative embodiments. A given such article of manufacture may comprise, for example, a storage array, a storage disk or an integrated circuit containing RAM, ROM, flash memory or other electronic memory, or any of a wide variety of other types of computer program products. The term “article of manufacture” as used herein should be understood to exclude transitory, propagating signals.

Also included in the processing device is network interface circuitry, which is used to interface the processing device with the network and other system components, and may comprise conventional transceivers.

As another example, portions of a given processing platform in some embodiments can comprise converged infrastructure such as VxRail™, VxRack™, VxRack™ FLEX, VxBlock™ or Vblock® converged infrastructure from Dell Technologies.

Again, these particular processing platforms are presented by way of example only, and other embodiments may include additional or alternative processing platforms, as well as numerous distinct processing platforms in any combination, with each such platform comprising one or more computers, servers, storage devices or other processing devices.

It should therefore be understood that in other embodiments different arrangements of additional or alternative elements may be used. At least a subset of these elements may be collectively implemented on a common processing platform, or each such element may be implemented on a separate processing platform.

Also, numerous other arrangements of computers, servers, storage devices or other components are possible in an information processing system as disclosed herein. Such components can communicate with other elements of the information processing system over any type of network or other communication media.

As indicated previously, components of an information processing system as disclosed herein can be implemented at least in part in the form of one or more software programs stored in memory and executed by a processor of a processing device. For example, at least portions of the functionality of host devices 102, SAN 104 and storage array 105 are illustratively implemented in the form of software running on one or more processing devices. As a more particular example, the instances of path selection logic 114 and IO throttling logic 115 may be implemented at least in part in software, as indicated previously herein.

It should again be emphasized that the above-described embodiments are presented for purposes of illustration only. Many variations and other alternative embodiments may be used. For example, the disclosed techniques are applicable to a wide variety of other types of information processing systems, utilizing other arrangements of host devices, networks, storage systems, storage arrays, storage devices, processors, memories, IO queues, MPIO drivers, path selection logic, initiators, targets, IO throttling logic, interface logic, data structures, and additional or alternative components. Also, the particular configurations of system and device elements and associated processing operations illustratively shown in the drawings can be varied in other embodiments. For example, a wide variety of different host device and storage system configurations and associated arrangements for detection and mitigation of slow drain issues can be used in other embodiments. Moreover, the various assumptions made above in the course of describing the illustrative embodiments should also be viewed as exemplary rather than as requirements or limitations. Numerous other alternative embodiments within the scope of the appended claims will be readily apparent to those skilled in the art. 

What is claimed is:
 1. An apparatus comprising: at least one processing device comprising a processor coupled to a memory; wherein the at least one processing device is configured: to control delivery of input-output operations from a host device to a storage system over selected ones of a plurality of paths through a network; to monitor response times for particular ones of the input-output operations sent from the host device to the storage system; responsive to at least a subset of the monitored response times being above a threshold over a time period, to generate an alert; to send the alert to an intermediary device coupled to the host device and the storage system; to receive from the intermediary device a throttling command generated in the intermediary device based at least in part on the alert; and responsive to receipt of the throttling command, to at least temporarily reduce a rate at which additional ones of the input-output operations are sent from the host device to the storage system.
 2. The apparatus of claim 1 wherein the at least one processing device comprises at least a portion of the host device.
 3. The apparatus of claim 1 wherein the paths are associated with respective initiator-target pairs, the initiators being implemented on the host device and the targets being implemented on the storage system, the initiators of the initiator-target pairs comprising respective host bus adaptors of the host device and the targets of the initiator-target pairs comprising respective storage array ports of the storage system.
 4. The apparatus of claim 1 wherein the throttling command is generated in the intermediary device based at least in part on identification in the intermediary device of one or more of the plurality of paths that each exhibits at least a threshold amount of mismatch between a negotiated rate of its initiator and a negotiated rate of its target.
 5. The apparatus of claim 4 wherein the mismatch between the negotiated rate of the initiator and the negotiated rate of the target comprises the negotiated rate of the initiator being less than the negotiated rate of the target.
 6. The apparatus of claim 1 wherein said at least one processing device is further configured to send negotiated rate information of respective initiators of the host device to the intermediary device for utilization by the intermediary device in generating the throttling command.
 7. The apparatus of claim 1 wherein said at least one processing device comprises a multi-path input-output driver of the host device, with the multi-path input-output driver of the host device being configured to control the delivery of the input-output operations from the host device to the storage system over the selected ones of the plurality of paths through the network.
 8. The apparatus of claim 7 wherein the multi-path input-output driver is further configured to perform at least a portion of the monitoring of response times, the generating of the alert, the sending of the alert, the receiving of the throttling command, and the at least temporarily reducing of the rate.
 9. The apparatus of claim 7 wherein the intermediary device comprises a multi-path input-output management station that is coupled to the multi-path input-output driver of the host device and to multi-path input-output drivers of respective ones of one or more additional host devices coupled to the storage system.
 10. The apparatus of claim 1 wherein the intermediary device comprises at least one server configured to obtain negotiated rate information for respective initiators from the host device and one or more additional host devices coupled to the storage system, and to obtain negotiated rate information for respective targets from the storage system, for utilization by the intermediary device in generating the throttling command.
 11. The apparatus of claim 1 wherein the intermediary device obtains negotiated rate information for respective initiators from the host device via an operating system (OS) native command line interface (CLI).
 12. The apparatus of claim 1 wherein the intermediary device obtains negotiated rate information for respective targets from the storage system via a representational state transfer (REST) call to the storage system.
 13. The apparatus of claim 1 wherein the throttling command is generated in the intermediary device responsive to a determination that the host device exhibits a greater degree of mismatch between one or more of its initiator negotiated rates and one or more corresponding target negotiated rates of the storage system than at least one other host device coupled to the storage system.
 14. The apparatus of claim 1 wherein said at least one processing device is further configured: to receive from the intermediary device an additional command generated in the intermediary device; and responsive to receipt of the additional command, to at least partially reverse the reduction in the rate at which additional ones of the input-output operations are sent from the host device to the storage system.
 15. A computer program product comprising a non-transitory processor-readable storage medium having stored therein program code of one or more software programs, wherein the program code, when executed by at least one processing device comprising a processor coupled to a memory, causes the at least one processing device: to control delivery of input-output operations from a host device to a storage system over selected ones of a plurality of paths through a network; to monitor response times for particular ones of the input-output operations sent from the host device to the storage system; responsive to at least a subset of the monitored response times being above a threshold over a time period, to generate an alert; to send the alert to an intermediary device coupled to the host device and the storage system; to receive from the intermediary device a throttling command generated in the intermediary device based at least in part on the alert; and responsive to receipt of the throttling command, to at least temporarily reduce a rate at which additional ones of the input-output operations are sent from the host device to the storage system.
 16. The computer program product of claim 15 wherein the intermediary device comprises at least one server configured to obtain negotiated rate information for respective initiators from the host device and one or more additional host devices coupled to the storage system, and to obtain negotiated rate information for respective targets from the storage system, for utilization by the intermediary device in generating the throttling command.
 17. The computer program product of claim 15 wherein the throttling command is generated in the intermediary device responsive to a determination that the host device exhibits a greater degree of mismatch between one or more of its initiator negotiated rates and one or more corresponding target negotiated rates of the storage system than at least one other host device coupled to the storage system.
 18. A method comprising: controlling delivery of input-output operations from a host device to a storage system over selected ones of a plurality of paths through a network; monitoring response times for particular ones of the input-output operations sent from the host device to the storage system; responsive to at least a subset of the monitored response times being above a threshold over a time period, generating an alert; sending the alert to an intermediary device coupled to the host device and the storage system; receiving from the intermediary device a throttling command generated in the intermediary device based at least in part on the alert; and responsive to receipt of the throttling command, at least temporarily reducing a rate at which additional ones of the input-output operations are sent from the host device to the storage system.
 19. The method of claim 18 wherein the intermediary device comprises at least one server configured to obtain negotiated rate information for respective initiators from the host device and one or more additional host devices coupled to the storage system, and to obtain negotiated rate information for respective targets from the storage system, for utilization by the intermediary device in generating the throttling command.
 20. The method of claim 18 wherein the throttling command is generated in the intermediary device responsive to a determination that the host device exhibits a greater degree of mismatch between one or more of its initiator negotiated rates and one or more corresponding target negotiated rates of the storage system than at least one other host device coupled to the storage system. 